Detecting URI in IIS

[blueclef]

I have developed a blogging page. It is working perfectly fine but I have a problem in presenting/accessing it. Blogs can be accessed by typing "www.mywebsitename.com/blog?id=5" for example. I need a way to rewrite this in a format like "www.bloggername.mywebsite.com". How do we go about doing it in PHP? I use IIS-5 and PHP 4.3.2. Please don't suggest URL-rewriters, etc. I want this done in proper PHP language. I tried $_SERVER["REQUEST_URI"] with no results. All I need is a way to figure out the URI that the user type, so that I could redirect him to the respect blog page.